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CVE Record

CVE-2026-81094: mcp-router CLI before 0.6.3 Binds the MCP Aggregator to All Interfaces Without Requiring Authentication

The mcp-router CLI served its MCP aggregator on every interface and enforced authentication only when the operator asked for it. The serve command in apps/cli/src/commands/serve.ts defaulted its host to the all-interfaces address on a fixed port, and required a token only when the corresponding flag was supplied, so a default invocation exposed the aggregator, and every MCP server it fronted, to anyone able to reach the port. Release 0.6.3 defaults the host to the loopback address and refuses to start without a token whenever the host it is given is not a loopback address; no earlier release carries either check.

CriticalCVSS 9.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

mcp-router CLI versions before 0.6.3 can unintentionally expose an MCP aggregator and its connected MCP servers over the network without authentication. A default launch may therefore allow any network-reachable party to access sensitive MCP capabilities or data. Version 0.6.3 changes the safe defaults and adds an authentication safeguard for non-loopback hosting.

Executive priority

Prioritize remediation immediately for internet-facing, cloud-hosted, shared-network, or otherwise untrusted-reachable instances. Upgrade all remaining pre-0.6.3 deployments promptly because default operation is unsafe and may expose downstream MCP services. Investigate reachable historical deployments for unauthorized access, while recognizing that the supplied evidence does not confirm exploitation.

Technical view

The serve command defaulted to an all-interfaces address on a fixed port, while token authentication was optional. This creates a network-accessible, unauthenticated endpoint under default settings. CVE-2026-81094 is rated CVSS 4.0 9.3 and CWE-306. Release 0.6.3 defaults to loopback and rejects non-loopback hosting without a token.

Likely exposure

Highest exposure exists where mcp-router CLI before 0.6.3 runs with default settings and the listening port is reachable from untrusted networks. Risk also extends to every MCP server fronted by that aggregator. Loopback-only or effectively firewalled instances have lower practical exposure, but still require configuration and version verification.

Exploitation context

The supplied sources establish low-complexity, unauthenticated network access with no user interaction. They do not establish observed exploitation, and the record is not identified as being in KEV. Treat internet-accessible or broadly reachable instances as urgent exposure without representing exploitation as confirmed.

Researcher notes

The vulnerable behavior is the combination of all-interface default binding and optional authentication. The confidentiality and integrity impacts are rated high; availability impact is not claimed in the supplied vector. Exposure depends on routing, firewalling, bind configuration, token use, and downstream MCP capabilities. Earlier releases lack both safeguards introduced in 0.6.3.

Mitigation direction

  • Upgrade mcp-router CLI to version 0.6.3 or later.
  • Bind the aggregator to loopback unless remote access is explicitly required.
  • Require a strong token whenever hosting on a non-loopback address.
  • Restrict aggregator access through network controls to trusted systems only.
  • Review current vendor guidance before relying on compensating controls.

Validation and detection

  • Inventory all mcp-router CLI deployments and record their installed versions.
  • Confirm each aggregator's effective listening address and network reachability.
  • Verify non-loopback instances cannot start or operate without token authentication.
  • Identify every MCP server exposed through each affected aggregator.
  • Review network telemetry for unexpected connections to previously reachable aggregators.
Prepared
Confidence
high
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-306: Credential and account abuse lookup

Authentication and credential weaknesses can make valid-account abuse and credential telemetry useful review starting points. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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description · low confidence lookup

Credential and access behavior lookup

The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-81094 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.3 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
3Timeline events
1ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.3CVSS 4.0CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N——VulnCheck
9.1CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N3.95.2VulnCheck

Vulnerability scoring details

Base CVSS 4.0 score

9.3Critical
CVSS 4.0 vector shape for CVE-2026-81094Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
mcp-routermcp-router0, 4c4642cfd274097ec8b33ecd3047390829c79d35unaffected
Weakness

CWE details

CWE-306

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-306 · source CWE mapping

CWE mapping pending import

This CVE carries a CWE mapping that will resolve to a full Glexia CWE intelligence page after the official CWE import is complete.

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